AZURITE
is a variety of carbonate of copper which shows various shades of
azure, merging into Berlin blue. Azurite is both opaque and
soft—hardness, 4—and these characteristics limit its use for gem
purposes.
BENITOITE.
A newly discovered gem mineral of California, blue in colour, and
said, when selected crystals are cut in the right direction, to rival
the sapphire in colour and to excel the blue corundum gem in
brilliancy. The mineral" is dichroic, the ordinary ray colourless, the
extraordinary ray blue. Benitoite crystallises in the hexagonal
system, trigonal division; its most common habit is pyramidal;
cleavage, imperfect pyramidal; fracture, conchoidal to sub-conchoidal;
hardness, 6 to 6-1/2; highly refractive. Benitoite fuses to a
transparent glass at about 3. It is easily attacked by hydrofluoric
acid. Chemically, benitoite is a very acid titano-silicate of barium.
Benitoite was discovered in 1907 by Mr. Hawkins and T. Edwin Sanders in
the Mt. Diabolo range near the San Benito-Fresno County line. The
mineral was determined at the University of California, and is
described in a bulletin of its geological department by George Davis
Louderback and Walter C. Blasdale.
